Acrylic copolymers exhibiting nonlinear optical response

ABSTRACT

This invention provides novel isotropic acrylic copolymers which exhibit nonlinear optical response, and which have utility as a transparent optical component in optical light switch and light modulator devices. 
     An invention isotropic acrylic copolymer is illustrated by the following structure: ##STR1##

This invention was made with Government support under Contract NumberF49620-86-C-0129 awarded by the Department of Defense. The FederalGovernment has certain rights in this invention.

The subject matter of this patent application is related to thatdisclosed in patent application Ser. No. 915,179, filed Oct. 3, 1986,which is incorporated herein by reference; patent application Ser. No.106,301, filed Oct. 9, 1987; and patent application Ser. No. 120,253,filed Nov. 10, 1987.

BACKGROUND OF THE INVENTION

It is known that organic and polymeric materials with large delocalizedπ-electron systems can exhibit nonlinear optical response, which in manycases is a much larger response than by inorganic substrates.

In addition, the properties of organic and polymeric materials can bevaried to optimize other desirable properties, such as mechanical andthermoxidative stability and high laser damage threshold, withpreservation of the electronic interactions responsible for nonlinearoptical effects.

Thin films of organic or polymeric materials with large second ordernonlinearities in combination with silicon-based electronic circuitryhave potential as systems for laser modulation and deflection,information control in optical circuitry, and the like.

Other novel processes occurring through third order nonlinearity such asdegenerate four-wave mixing, whereby real-time processing of opticalfields occurs, have potential utility in such diverse fields as opticalcommunications and integrated circuit fabrication.

Of particular importance for conjugated organic systems is the fact thethe origin of the nonlinear effects is the polarization of theπ-electron cloud as opposed to displacement or rearrangement of nuclearcoordinates found in inorganic materials.

Nonlinear optical properties of organic and polymeric materials was thesubject of a symposium sponsored by the ACS division of PolymerChemistry at the 18th meeting of the American Chemical Society,September 1982. Papers presented at the meeting are published in ACSSymposium Series 233, American Chemical Society, Washington, D.C. 1983.

The above recited publications are incorporated herein by reference.

Of more specific interest with respect to the present inventionembodiments is prior art relating to polymers with comb-like sidechains. Eur. Polym. J., 18, 651(1982) describes liquid crystallinepolymers of the smectic and nematic types with cyanobiphenyl groups inthe side chain: ##STR2## where R is hydrogen or methyl, n is an integerof 2-11, and X is an oxy, alkylene or carbonyloxy divalent radical.

SPIE Vol. 682, pages 56-64, Molecular and Polymeric OptoelectronicMaterials: Fundamentals and Applications (presented at Aug. 21-22, 1986meeting) describes liquid crystalline polymeric systems which arecopolymers of a mesogenic monomer and a nonlinear optically responsivemonomer.

A disadvantage of liquid crystalline polymers which exhibit mesogenicside chain nonlinear optical response is an observed light scatteringeffect when the polymer is in the form of a solid phase optical medium,e.g., the polymer medium exhibits more than about 20 percent scatteringof transmitted incident light. The light scattering is due to deviationsfrom ideal molecular order which accommodate defects that are notoptically clear.

There is continuing interest in the theory and practice of polymerswhich are characterized by comb-like side chain structures which can beoriented in an applied external field.

There is also an increasing research effort to develop new nonlinearoptical organic systems for prospective novel phenomena and devicesadapted for laser frequency conversion, information control in opticalcircuitry, light valves and optical switches. The potential utility oforganic materials with large second order and third order nonlinearitiesfor very high frequency application contrasts with bandwidth limitationsof conventional inorganic electrooptic materials.

Accordingly, it is an object of this invention to provide novel polymerswith comb-like side chains.

It is another object of this invention to provide acrylic copolymershaving side chains which exhibit nonlinear optical response.

It is a further object of this invention to provide optical light switchand light modulator devices with a transparent polymeric nonlinearoptical component comprising an isotropic acrylic copolymer.

Other objects and advantages of the present invention shall becomeapparent from the accompanying description and examples.

DESCRIPTION OF THE INVENTION

One or more objects of the present invention are accomplished by theprovision of an isotropic acrylic copolymer which is characterized byrecurring monomeric units corresponding to the formula: ##STR3## where mand m¹ are integers which total at least 10, and the m monomer comprisesbetween about 10-90 mole percent of the total m+m¹ monomer units; R ishydrogen or a C₁ -C₄ alkyl , C₆ -C₁₀ aryl, halo or haloalkylsubstituent; R is a C₁ -C₆ alkyl substituent; and Z is a nitro or cyanosubstituent.

In another embodiment this invention provides a transparent nonlinearoptical medium comprising an isotropic acrylic copolymer having astructure as represented in the above formula.

In another embodiment this invention provides a transparent nonlinearoptical medium comprising an acrylic copolymer having a structure asrepresented in the above formula, and being further characterized by anexternal field-induced orientation of aligned m monomer side chains.

In another embodiment this invention provides an isotropic acryliccopolymer which is characterized by recurring monomeric unitscorresponding to the formula: ##STR4## where m and m¹ are integers whichtotal at least 20, and the m monomer comprises between about 20-80 molepercent of the total m+m¹ monomer units; R' is hydrogen or a methylsubstituent; and R¹ is a C₁ -C₆ alkyl substituent.

In another embodiment this invention provides an isotropic acryliccopolymer which is characterized by recurring monomeric unitscorresponding to the formula: ##STR5## where m and m¹ are integers whichtotal at least 20, and the m monomer comprises between about 20-80 molepercent of the total m+m¹ monomer units; R' is hydrogen or a methylsubstituent; and R¹ is a C₁ -C₆ alkyl substituent.

In a further embodiment this invention provides an optical light switchor light modulator device with a polymeric nonlinear optical componentcomprising a transparent solid medium of an isotropic acrylic copolymerwhich is characterized by recurring monomeric units corresponding to theformula: ##STR6## where m and m¹ are integers which total at least 10,and the m monomer comprises between about 10-90 mole percent of thetotal m+m¹ monomer units; R is hydrogen or a C₁ -C₄ alkyl, C₆ -C₁₀ aryl,halo or haloalkyl substituent; R¹ is a C₁ -C₆ alkyl substituent; and Zis a nitro or cyano substituent.

Illustrative of C₁ -C₄ and C₁ -C₆ alkyl substituents in the abovedefined polymer formulae are methyl, ethyl, propyl, isopropyl, butyl,isobutyl, pentyl, hexyl, 2-hexyl, and the like.

Illustrative of C₆ -C₁₀ aryl substituents are phenyl, tolyl, xylyl,methoxyphenyl, chlorophenyl, naphthyl, and the like.

Illustrative of halo and haloalkyl substituents are chloro, bromo,fluoro, trifluoromethyl, and the like.

A present invention isotropic acrylic copolymer can contain other vinylcomonomeric units in addition to the acrylate units. Illustrative ofcopolymerizable vinyl monomers are vinyl halide, vinyl carboxylate,acrylonitrile, methacrylonitrile, alkene, arylvinyl, and the like.Suitable vinyl monomers include vinyl chloride, vinyl acetate, ethylene,propylene, isobutylene, isoprene and styrene.

The additional vinyl comonomer or comonomers can be incorporated in aproportion up to about 30 mole percent of a present invention isotropicacrylic copolymer.

A present invention isotropic acrylic copolymer normally has a glasstransition temperature in the range between about 40°-180° C., and aweight average molecular weight in the range between about 5000-200,000.

A present invention isotropic acrylic copolymer has a glass-likeappearance which is optically transparent in both solid and melt phases.An invention copolymer is tractable, and the relatively low viscosity ofthe melt phase facilitates induced orientation of the copolymer sidechains by means of an external field.

The term "isotropic" as employed herein refers to an acrylic copolymerwhich in the form of a transparent medium exhibits optical propertieswhich are equivalent in all tensor directions.

The term "transparent" as employed herein refers to an optical mediumwhich is transparent or light transmitting with respect to incidentfundamental light frequencies and created light frequencies. In anonlinear optical device, a present invention polymeric nonlinearoptical component is transparent to both the incident and exit lightfrequencies, and the polymeric nonlinear optical component exhibits lessthan about 5 percent scattering of transmitted incident light.

A present invention optical light switch or light modulator devicetypically will have a polymeric nonlinear optical component which is atransparent solid medium of an isotropic acrylic copolymer having astable orientation of an external field-induced alignment of pendantside chains.

Illustrative of a present invention optical device containing apolymeric nonlinear optical component as defined above is a laserfrequency converter, an optical Pockels effect device, an optical Kerreffect device, a degenerate four wave mixing device, an opticalinterferometric waveguide gate, a wide-band electrooptical guided waveanalog-to-digital converter, an all-optical multiplexer, an all-opticaldemultiplexer, an optical bistable device, or an optical parametricdevice.

Optical harmonic generating devices are described in Science, 216(1982);and in U.S. Pat. Nos. 3,234,475; 3,395,329; 3,694,055; 3,858,124; and4,536,450.

Optical Kerr effect devices are described in U.S. Pat. Nos. 4,428,873and 4,515,429; and references cited therein.

Degenerate four wave mixing optical devices are discussed by Y. R. Shenin Chapter 15, "The Principles of Nonlinear Optics"; John Wiley & Sons,New York (1984). A nonresonant degenerate four wave mixing mirror deviceis described by J. Feinberg et al in Optics Letters, 5(12), 519(1980).

An optical interferometric waveguide gate device is described by A.Lattes et al in IEEE J. Quantum Electron, QE-19(11), 1718(1983).

A wide-band electrooptical guided-wave analog-to-digital converterdevice is described by R. A. Becker et al in Proceedings Of The IEEE,72(7), 802(1984).

Optical multiplexer-demultiplexer devices are described in U.S. Pat.Nos. 3,532,890; 3,755,676; 4,427,895; 4,455,643; and 4,468,776.

Optical bistable devices are described in U.S. Pat. Nos. 4,515,429 and4,583,818; and by P. W. Smith et al in Applied Physics Letters, 30(6),280(1977), and in IEEE Spectrum, June 1981.

Optical parametric devices are described in U.S. Pat. Nos. 3,371,220;3,530,301; and 3,537,020.

A present invention optical device can be provided by constructing anoptical device of the type described in the technical literature, exceptthat a novel isotropic acrylic copolymer as defined herein is utilizedas the nonlinear optical component.

Synthesis of Isotropic Acrylic Copolymers

The preparation of isotropic acrylic copolymers with nonlinear opticallyresponsive side chains is illustrated by the following flow diagram:##STR7##

Nonlinear Optical Properties

The fundamental concepts of nonlinear optics and their relationship tochemical structures can be expressed in terms of dipolar approximationwith respect to the polarization induced in an atom or molecule by an anexternal field.

As summarized in the ACS Symposium Series 233(1983) listed hereinabovein the Background Of The Invention section, the fundamental equation (1)below describes the change in dipole moment between the ground stateμ_(g) and an excited state μ_(e) expressed as a power series of theelectric field E which occurs upon interaction of such a field, as inthe electric component of electromagnetic radiation, with a singlemolecule. The coefficient α is the familiar linear polarizability, β andγ are the quadratic and cubic hyperpolarizabilities, respectively. Thecoefficients for these hyperpolarizabilities are tensor quantities andtherefore highly symmetry dependent. Odd order coefficients arenonvanishing for all structures on the molecular and unit cell level.The even order coefficients such as β are zero for those structureshaving a center of inversion symmetry on the molecular and/or unit celllevel.

Equation (2) is identical with (1) except that it describes amacroscopic polarization, such as that arising from an array ofmolecules in an isotropic polymer domain:

    Δμ=μ.sub.e -μ.sub.g =αE+γEE+βEEE+. . . (1)

    P=P.sub.O +χ.sup.(1) E+χ.sup.(2) EE+χ.sup.(3) EEE+. . . (2)

Light waves passing through an array of molecules can interact with themto produce new waves. This interaction may be interpreted as resultingfrom a modulation in refractive index or alternatively as a nonlinearityof the polarization. Such interaction occurs most efficiently whencertain phase matching conditions are met, requiring identicalpropagation speeds of the fundamental wave and the harmonic wave.Birefringent crystals often possess propagation directions in which therefractive index for the fundamental ω and the second harmonic 2ω areidentical so that dispersion may be overcome.

The term "phase matching" as employed herein refers to an effect in anonlinear optical medium in which a harmonic wave is propagated with thesame effective refractive index as the incident fundamental light wave.Efficient second harmonic generation requires a nonlinear optical mediumto possess propagation directions in which optical medium birefringencecancels the dispersion as a function of wavelength, i.e., the opticaltransmission of fundamental and second harmonic frequencies is phasematched in the medium. The phase matching can provide a high conversionpercentage of the incident light to the second harmonic wave.

For the general case of parametric wave mixing, the phase matchingcondition is expressed by the relationship:

    n.sub.1 ω.sub.1 +n.sub.2 ω.sub.2 =n.sub.3 ω.sub.3

where n₁ and n₂ are the indexes of refraction for the incidentfundamental radiation, n₃ is the index of refraction for the createdradiation, ω₁ and ω₂ are the frequencies of the incident fundamentalradiation and ω₃ is the frequency of the created radiation. Moreparticularly, for second harmonic generation, wherein ω₁ and ω₂ are thesame frequency ω, and ω₃ is the created second harmonic frequency 2ω,the phase matching condition is expressed by the relationship:

    n.sub.107 =n.sub.2ω

where n₁₀₇ and n₂ω are indexes of refraction for the incidentfundamental and created second harmonic light waves, respectively. Moredetailed theoretical aspects are described in "Quantum Electronics" byA. Yariv, chapters 16-17 (Wiley and Sons, New York, 1975).

A present invention isotropic acrylic copolymer medium typically hasexcellent optical transparency and exhibits hyperpolarization tensorproperties such as second harmonic and third harmonic generation, andthe linear electrooptic (Pockels) effect. For second harmonicgeneration, the bulk phase of the acrylic polymer medium whether liquidor solid does not possess a real or orientational average inversioncenter. The substrate is a macroscopic noncentrosymmetric structure.

Harmonic generation measurements relative to quartz can be performed toestablish the value of second order and third order nonlinearsusceptibility of the optically clear substrates.

In the case of macroscopic nonlinear optical media that are composed ofnoncentrosymmetric sites on the molecular and domain level, themacroscopic second order nonlinear optical response χ.sup.(2) iscomprised of the corresponding molecular nonlinear optical response β.In the rigid lattice gas approximation, the macroscopic susceptibilityχ.sup.(2) is expressed by the following relationship:

    χ.sub.ijk (-ω.sub.3 ; ω.sub.1, ω.sub.2)=Nf.sup.ω3 f.sup.ω2 f.sup.ω1 <β.sub.ijk (-ω.sub.3 ; ω.sub.1, ω.sub.2)>

wherein N is the number of sites per unit volume, f represent smalllocal field correlations, B_(ijk) is averaged over the unit cell, ω₃ isthe frequency of the created optical wave, and ω₁ and ω₂ are thefrequencies of the incident fundamental optical waves.

A nonlinear optical medium with a centrosymmetric configuration ofpolymer molecules as defined herein can exhibit third order nonlinearoptical susceptibility χ.sup.(3) of at least about 1×10⁻¹⁰ esu asmeasured at 1.91 μm excitation wavelength.

A nonlinear optical medium with an external field-inducednoncentrosymmetric configuration of polymer molecules as defined hereincan exhibit second order nonlinear optical susceptibility χ.sup.(2) ofat least about 5×10⁻⁸ esu as measured at 1.91 μm excitation wavelength.

These theoretical considerations are elaborated by Garito et al inchapter 1 of the ACS Symposium Series 233 (1983); and by Lipscomb et alin J. Chem., Phys., 75, 1509 (1981), incorporated by reference. See alsoLalama et al, Phys. Rev., A20, 1179 (1979); and Garito et al, Mol.,Cryst. and Liq. Cryst., 106, 219 (1984); incorporated by reference.

External Field-Induced Side Chain Orientation

The term "external field" as employed herein refers to an electric,magnetic or mechanical stress field which is applied to a medium ofmobile organic molecules, to induce dipolar alignment of the moleculesparallel to the field.

The nonlinear optically responsive side chains of a present inventionacrylic copolymer may be aligned by the application of an external fieldto a mobile matrix of the acrylic copolymer molecules. Application of aDC electric field produces orientation by torque due to the interactionof the applied electric field and the net molecular dipole moment of thepolymer side chains. The molecular dipole moment is due to both thepermanent dipole moment (i.e., the separation of fixed positive andnegative charge) and the induced dipole moment (i.e., the separation ofpositive and negative charge by the applied field).

Application of an AC electric field also can induce bulk alignment. Inthis case, orienting torque occurs solely due to the interaction of theapplied AC field and the induced dipole moment. Typically, AC fieldstrengths exceeding 1 kV/cm at a frequency exceeding 1 KHz are employed.

Application of a magnetic field also can effect alignment. Organicmolecules do not possess a permanent magnetic dipole moment. In a manneranalogous to AC electric field, a magnetic field can induce a netmagnetic dipole moment. Torque results from the interaction of theinduced dipole moment and the external magnetic field. Magnetic fieldstrengths exceeding 10 Kgauss are sufficient to induce alignment ofmobile acrylic copolymer side chains.

Mechanical stress induced molecular alignment is applicable to sidechain acrylic copolymers. Specific mechanical stress methods includestretching a thin film, or coating an acrylic copolymer surface with analigning polymer such as nylon. Physical methods (e.g., stretching) relyupon the rigid and geometrically asymmetric character of the acryliccopolymer molecules to induce bulk orientation. Chemical methods (e.g.,coating the surface with an aligning polymer) rely upon strongintermolecular interactions to induce surface orientation.

Application of an AC electric, magnetic or mechanical external fieldproduces colinear molecular alignment in which the molecular direction(either parallel or antiparallel to the orientation axis) isstatistically random, and the resultant molecularly oriented mediumexhibits third order nonlinear optical susceptibility χ.sup.(3).Application of a DC electric external field produces colinear molecularalignment in which the molecular direction is not random, and ischaracterized by a net parallel alignment of molecular dipoles. Theresultant molecularly oriented medium exhibits second order nonlinearoptical susceptibility χ.sup.(2).

The orientation of the isotropic acrylic copolymer side chains isaccomplished when the polymer molecules are in a mobile phase, e.g., thecopolymer is at a temperature near or above the copolymer glasstransition temperature. The aligned phase of the mobile molecules can befrozen by cooling the medium below the glass transition temperaturewhile the aligned phase is still under the influence of the appliedexternal field.

The following examples are further illustrative of the presentinvention. The components and specific ingredients are presented asbeing typical, and various modifications can be derived in view of theforegoing disclosure within the scope of the invention.

EXAMPLE I

This Example illustrates the preparation of an iostropic 50/50 copolymerof 4-[4-methacroyloxypiperidyl]-4'-nitrostilbene and butyl methacrylate.##STR8##

A. 4-(4-Hydroxypiperidyl)benzaldehyde

A 2 liter three necked flask fitted with a mechanical stirrer,thermometer and condenser is charged with 180 g of 4-hydroxypiperidine,74.4 g of 4-fluorobenzaldehyde, 1 ml of Aliquat 336, 750 ml ofdimethylsulfoxide and 82.8 g of anhydrous potassium carbonate. Themixture is heated at 95° C. for three days, then the product mixture iscooled and poured into 3 liters of ice water. The resultant solidprecipitate is filtered, washed with water, and vacuum dried. The crudeproduct is recrystallized from toluene, m.p. 115°-118° C.

B. 4-(4-Hydroxypiperidyl)-4'-nitrostilbene

A one liter three necked flask fitted with a dropping funnel, mechanicalstirrer and condenser is charged with 34.35 g of 4-nitrophenylaceticacid. Piperidine (16.2 g) is added dropwise over a period of 30 minutes.At the end of the addition, 38.4 g of 4-(4-hydroxypiperidyl)benzaldehydeis added. The reaction mixture is heated at 100° C. for three hours, andat 130° C. for three hours. After cooling, the semi-solid product massis ground in ethanol in a blender, then filtered, washed, and vacuumdried. The crude product is recrystallized from chlorobenzene, m.p.248°-250° C.

C. 4-(4-Methacroyloxypiperidyl)-4'-nitrostilbene

A one liter three necked flask fitted with a thermometer, condenser,dropping funnel with argon inlet, and magnetic stirrer, is charged with5 g of 4-(4-hydroxypiperidyl)-440 -nitrostilbene, 5 g of triethylamineand 400 ml of dichloromethane. The mixture is heated to 35° C., and 3.2g of methacroyl chloride is added dropwise over a 30 minute period.After stirring at 35° C. for 4 hours, another 3.2 g of methacroylchlrride is added, and the mixture is stirred for about 18 hours at 35°C. The product mixture then is extracted three times with distilledwater, and the organic phase is dried over magnesium sulfate, and thesolvent is evaporated. The resultant crude product is recrystallizedfrom acetonitrile, m.p. 175°-176° C.

D. 50/50 Isotropic Acrylic Copolymer

4-(4-Methacroyloxypiperidyl)-4'-nitrostilbene (2g) is suspended in 20 mlof chlorobenzene, and the mixture is degassed one hour. To thesuspension are added 0.724 g of butyl methacrylate (7.24 ml of a 10%solution in chlorobenzene) and one mole percent ofazobisisobutyronitrile.

The reactor is capped and placed in a 75° C. oil bath for a period ofabout 18 hours. The product mixture then is poured into methanol toprecipitate the copolymer. The solid copolymer is recovered byfiltration, and vacuum dried.

The polymer has a weight average molecular weight in the range of60,000-80,000, and exhibits a T_(g) of 150° C.

EXAMPLE II

This Example illustrates the preparation of isotropic acrylic copolymersand terpolymers in accordance with the present invention.

The procedures of Example I are followed, employing selectedcombinations of monomers.

A 25/75 copolymer of 4-(4-methacroyloxypiperidyl)-4'-nitrostilbene andbutyl methacrylate has a weight average molecular weight in the range of60,000-80,000, and exhibits a T_(g) of 91.5° C.

A 25/75 copolymer of 4-(4-methacroyloxypiperidyl)-4'-nitrostilbene andmethyl methacrylate has a weight average molecular weight in the rangeof 60,000-80,000, and exhibits a T_(g) of 144° C.

Utilizing the Example I procedures, the following copolymers andterpolymers are prepared:

(50/50) 4-[4-(2-fluoro)acroyloxypiperidyl]-4'-cyanostilbene/methylacrylate

(90/10) 4-[4-(2-phenyl)acroyloxypiperidyl]-4'-nitrostilbene/methylmethacrylate

(30/70)4-[4-(2-trifluoromethyl)acroyloxypiperidyl]-4'-nitrostilbene/hexylacrylate

(50/50) 4-(4-methacroyloxypiperidyl)-4'-nitrostilbene/methyl2-(4-methylphenyl)acrylate

(75/12.5/12.5) 4-(4-acroyloxypiperidyl)-4'-nitrostilbene/methylacrylate/styrene

The prepared polymers have a combination of physical and opticalproperties which are similar to those of the isotropic acrylic copolymerdescribed in Example I.

EXAMPLE III

This Example illustrates a poling procedure for producing a transparentfilm of an isotropic side chain acrylic copolymer which exhibits secondorder nonlinear optical response in accordance with the presentinvention.

A. Poling Cell Construction

A poling cell is constructed using an electrically conductive glassplate as a substrate, such as Corning Glass EC-2301. The glass plate iswashed with sulfuric acid, isopropanol, 1-dodecanol, and isopropanol,with a distilled water rinse between each washing step.

A thin film of a buffer layer of polysiloxane of 0.8 micron thickness isdeposited by a spin coating process on the cleaned conductive glassplate. The spin coating process involves covering the glass plate with a10% by weight solution of polysiloxane in isobutanol, spinning the glassat a rotational speed of 3500 rpm, and then drying the film at 120° C.for 4 hours in a nitrogen atmosphere.

When the lower buffer layer film is sufficiently hardened, a thin filmof 2 micron thickness of the Example II 25/75 copolymer of4-(4-methacroyloxypiperidyl)-4'-nitrostilbene and butyl methacrylate isdeposited on the buffer film by spin coating. The spin coating inaccomplished by covering the buffer surface with a 15% by weightsolution of the polymer in 1,2,3-trichloropropane, spinning at 2000 rpm,and then drying the film at 110° C. for 16 hours in a nitrogenatmosphere.

Another buffer layer of 0.8 microns of polysiloxane is deposited on topof the hardened polymer film by spin coating. On the hardened upperlayer, a thin layer of gold of about 1000 Angstrom thickness isdeposited using a thermal evaporation process. A gold thin film isemployed as one of then are attached to the conductive glass plate andthe gold film utilizing electrically conductive epoxy adhesive.

B. Electric Field-Induced Orientation

The poling assembly is placed in a microscope hot stage (Mettler FP-82with FP-80 Central Processor), and the sample is observed with apolarizing microscope (Leitz Ortholux Pol) for alignment. The two leadwires are connected to a DC voltage source (Kepco OPS-3500), whichgenerates a voltage signal up to 3500 V.

The poling cell is first heated to 100° C. to bring the acryliccopolymer to the melt phase. The DC voltage source is slowly turned upto 400 V. The field strength is calculated to be approximately 1.1×10⁶V/cm. The sample is maintained at this field strength level for a periodof about two seconds or longer as necessary to achieve the molecularalignment. This is followed by a rapid cooling to about 30° C. while thefield is still applied. When the sample reaches 30° C., the voltagesource is disconnected. A noncentrosymmetrically oriented acryliccopolymer matrix is obtained by the poling procedure.

The χ.sup.(2) value for the acrylic copolymer nominally is 165×10⁻⁹ esuas measured at 1.34 micron excitation wavelength laser. A comparativeχ.sup.(2) value for potassium hydrogen phosphate is 2.4×10⁻⁹ esu.

What is claimed is:
 1. An isotropic acrylic copolymer which ischaracterized by recurring monomeric units corresponding to the formula:##STR9## where m and m¹ are integers which total at least 10, and the mmonomer comprises between about 10-90 mole percent of the total m+m¹monomer units; R is hydrogen or a C₁ -C₄ alkyl, C₆ -C₁₀ aryl, halo orhaloalkyl substituent; R¹ is a C₁ -C₆ alkyl substituent; and Z is anitro or cyano substituent.
 2. An acrylic copolymer in accordance withclaim 1 which has a weight average molecular weight in the range betweenabout 5000-200,000.
 3. An acrylic copolymer in accordance with claim 1which has a glass transition temperature in the range between about40°-180° C.
 4. A transparent nonlinear optical medium comprising acopolymer in accordance with claim
 1. 5. A transparent nonlinear opticalmedium in accordance with claim 4 which is characterized by an externalfield-induced orientation of aligned m monomer side chains.
 6. Anisotropic acrylic copolymer which is characterized by recurringmonomeric units corresponding to the formula: ##STR10## where m and m¹are integers which total at least 20, and the m monomer comprisesbetween about 20-80 mole percent of the total m+m¹ monomer units; R' ishydrogen or a methyl substituent; and R¹ is a C₁ -C₆ alkyl substituent.7. A transparent nonlinear optical medium comprising an acryliccopolymer in accordance with claim
 6. 8. A transparent nonlinear opticalmedium in accordance with claim 7 which is characterized by an externalfield-induced orientation of aligned m monomer side chains.
 9. Anisotropic acrylic copolymer which is characterized by recurringmonomeric units corresponding to the formula: ##STR11## where m and m¹are integers which total at least 20, and the m monomer comprisesbetween about 20-80 mole percent of the total m+m¹ monomer units; R' ishydrogen or a methyl substituent; and R¹ is a C₁ -C₆ alkyl substituent.10. A transparent nonlinear optical medium comprising an acryliccopolymer in accordance with claim
 9. 11. A transparent nonlinearoptical medium in accordance with claim 10 which is characterized by anexternal field-induced orientation of aligned m monomer side chains. 12.An optical light switch or light modulator device with a polymericnonlinear optical component comprising a transparent solid medium of anisotropic acrylic copolymer which is characterized by recurringmonomeric units corresponding to the formula: ##STR12## where m and m¹are integers which total at least 10, and the m monomer comprisesbetween about 10-90 mole percent of the total m+m¹ monomer units; R ishydrogen or a C₁ -C₄ alkyl, C₆ -C₁₀ aryl, halo or haloalkyl substituent;R¹ is a C₁ -C₆ alkyl substituent; and Z is a nitro or cyano substituent.13. An optical device in accordance with claim 12 wherein the polymermedium exhibits second order nonlinear optical susceptibility χ.sup.(2).14. An optical device in accordance with claim 12 wherein the polymermedium exhibits third order nonlinear optical susceptibility χ.sup.(3).15. An optical device in accordance with claim 12 wherein the polymermedium has a stable orientation of an external field-induced alignmentof m monomer side chains.
 16. An optical device in accordance with claim12 wherein the polymeric component is an acrylic copolymer correspondingto the formula represented in claim
 6. 17. An optical device inaccordance with claim 12 wehrein the polymeric component is an acryliccopolymer corresponding to the formula represented in claim
 9. 18. Anoptical device in accordance with claim 12 wherein the polymericnonlinear optical component exhibits less than about 5 percentscattering of transmitted incident light.